(1) Field of the Invention
The present invention relates to a method of improving and increasing sustainable shear force capabilities at an interfacing surface between a rigid material and a flexible material.
(2) Description of the Prior Art
It is well known to utilize a resilient bushing having a pair of concentric rigid, typically metal sleeves. FIG. 1 is a prior art example of a typical fastening arrangement 10 utilizing adhesion at rigid-to-flexible interfacing surfaces. The inner sleeve 13 is secured to one structural component 15 (for example an input shaft) while the outer sleeve 18 is secured to another structural component 20 (for example a propeller shaft). An annular elastomeric insert 23 is concentrically positioned between the rigid sleeves 13, 18. The interface between the interfacing surfaces needs to transmit high shear and torque loads. Previous designs would fail locally in shear due the high torque applied during the functional application, and due to the comparatively low shear which these devices could sustain. Higher torque, shear, adhesion was needed at the rigid-to-flexible material interfaces. The adhesion resistance to shear failure at the surface interface 25 and 27 is what supports the full torque during operation.
In the past, most interfacing surfaces 25 and 27 were relatively smooth; that is, their surface roughness was generally less than 170 RMS as measured by SAE Standard J448a. A method of increasing adhesion resistance to shear failure was the addition of a phosphate coating of various thicknesses. However, the surface roughness did not exceed roughly 170 RMS.
A method and apparatus for improving resistance to adhesion failure between two interfacing surfaces utilizing by producing a particular shape and roughness is disclosed. The present invention utilizes both coarse and fine surface roughness producing techniques. The surface, to be treated, has a coarse (large scale) surface roughness component on the order of about three to four orders of magnitude greater than the fine (small scale) surface roughness component. The invention uses a plurality of superimposed roughnesses rather than one range of roughness, as seen in prior art. The appropriate surfaces of the rigid part are roughened (e.g., by machining, casting, molding, sandblasting) to yield surfaces having both small (fine) and large (coarse) scale roughness components. The large-scale roughness component is about three orders of magnitude greater than the small scale roughness component.
The object of this invention is to improve and increase sustainable shear force capabilities at an interfacing surface between a rigid material (for example: a structural metal) and a flexible material (for example: an elastomeric dampening material).
Another object of the present invention is to improve and increase the sustainable shear force capabilities at an interfacing surface without internal or external fastening devices such as bolts, screws, washers, and the like.
Yet another object of the present invention is to improve and increase the sustainable shear force capabilities at an interfacing surface in a smaller, more compact volume than previous methods.
Yet another object of the present invention is to improve and increase the sustainable shear force capabilities at an interfacing surface with a simplistic (that is without a large number of parts) and economy.